(a) Scope of the Invention
The present invention relates generally to a heat sensing device which is activated at a predetermined temperature, and more particularly, is directed to a heat sensor for use in fire alarm systems. It may contain means cooperatively associated therewith to sound an alarm.
(b) Prior Art Statement
Generally, heat detecting and sensing units, as presently designed, are responsive to the presence of heat in the relatively immediate environment in which they are located. They are generally designed for either a fixed temperature response or a rate of rise temperature response. The present invention is directed to the former type of system.
Heat detection and sensing responses to predetermined elevated temperatures have been accomplished in any number of ways, such as, for example, by obstructing a conduit between a compressed gas tank and an alarm sounding horn with a low melting temperature alloy such as eutectic solder. When the solder is fused, the obstruction is cleared and the alarm sounding apparatus is activated.
Such devices generally suffer from insensitivity and therefore, a larger number of such units are required to be installed to protect a given area. Most recently, efforts have been made to develop more sensitive heat sensors, an example of which is described in U.S. Pat. No. 4,052,690. This detection device utilizes a thin disk to collect and transmit heat to a eutectic solder which melts to actuate a valve. It is directed to a somewhat complex assembly requiring special attaching strips with insulative phenolic plastic portions. Some of the attaching strips are soldered with conventional 50-50 solder while others are soldered with eutectic solder. This type of sensor is disclosed as being utilized with an alarm system. Once the eutectic solder melts, the alarm sounds until all of the compressed gas is released; there is no provision for deactivating the alarm.
Another problem encountered by such systems is that they do not activate and/or sound an alarm at the earliest possible time since the response which activates the system does not positively trigger the alarm when the surrounding environment reaches the previously selected activating temperature. In many instances, this can be caused by a heat sensor which is not truely responsive to the surrounding environment, one in which the heat is not properly transmitted to the eutectic bonding material, and even more often, one in which the containment and release mechanisms for the eutectic bond are not properly designed to insure an early and positive release of the bond.